A Zinc-Air battery which takes oxygen molecules in the air as the cathode reactant has been considered as the substitute for an alkaline battery due to its features of high specific energy and outputting stable discharge voltages. Moreover, the application including the battery for an automobile, a hearing aid can also utilizes the Zinc-Air battery as a power supply device to increase the advantages of environmental protection and low price.
Since the type of the Zinc-Air battery uses zinc metal as an anode and oxygen in the air (O2) as a cathode, the cathode of the Zinc-Air battery is so called the air cathode. Potassium hydroxide (KOH) aqueous solution is taken as electrolyte inside the Zinc-Air battery. After the oxygen in the air undergoes the cathode chemical reaction to from hydroxyl ion (OH—), the zinc anode composed of the zinc mixture (zinc syrup, zinc plate or zinc foil) undergoes the oxygen reduction reaction to output stable discharge voltages. The chemical formula of the oxygen reduction reaction is listed as below:Cathode: H2O+½O2+2e−→2OH−Anode: Zn+2OH−→ZnO+H2O+2e−Reaction: Zn+½O2→ZnO
Since the air cathode of the Zinc-Air battery is only taken as the medium, its activity/mass may not be changed or used up. While manufacturing the Zinc-Air battery, the loading of the zinc anode of the Zinc-Air battery can be increased to increase the capacity and specific energy, thereby achieving the goal of miniaturizing the Zinc-Air battery.
However, this type of the Zinc-Air battery must be equipped with air holes to let air enter the battery. The housing of the Zinc-Air battery may not be sealed, and it must be made into the semi-open structure. The semi-open structure will influence the performances of the Zinc-Air battery and shorten the service life of the Zinc-Air battery since the Zinc-Air battery is easily influenced by air.
Further, the conventional air cathode structure utilized by the Zinc-Air battery employs the single layer structure that has a drawback of maintaining the water content of the zinc anode inside the battery for long period. If the outside air is at high humidity condition, water vapor may enter the inside of the Zinc-Air battery through the air cathode of the Zinc-Air battery, resulting in dilution of the electrolyte and reduction of the discharge voltage, and on the other if the outside air is at low humidity condition, the electrolyte inside the Zinc-Air battery may lose its water content through the air cathode. Consequently, the electrolyte may be run out and the battery may malfunction.
The conventional process for manufacturing the air cathode having the multilayer structure must sinter the multilayer structure composed of the diffusion layers and the substrate at high temperature after performing the pressing procedure to tighten the structure. The multilayer structure then is sintered again after catalyst layers are coated on the diffusion layers to cause inconvenience and high production cost.